If you and your SO aren't butt fucking ugly then I'll watch..
If you didn't want to do Oasis Aqualounge, then I'd cruise airport hotel bars.. Look for dude's in suits who are eating alone. They're likely there on business and would be a lot more open to this sorta thing (have less a chance of somebody they know seeing them)..
I might suggest you be extremely careful though (and explain to the dude exactly what your expectations are). If some couple invited me to watch them fuck, and the woman was looking me dead in the eye the whole time (or kept grinning at me or some shit), I might think I was being signaled to get tagged in.. This would become a very awkward situation..
All sorts of weird things have to be thought of.. Is the guy allowed to jack off? Can he feel your wife's tits? If he can feel her tits, can he spunk on them? Is he allowed to touch you (you really might want to clear this one up first..)..
It's not illegal to proposition somebody (no matter how lewd the act)...